As the object having image pattern, there are circuit substrate, mug, craftwork and so on. The circuit substrate is an object which is formed a circuit pattern on a surface thereof the mug is an object having a decoration image on outer circumferential surface of the cup which is made from ceramics, and many of craftworks are the objects formed an industrial art decoration image on the surface of industrial art articles. Since highly fine and densification of the circuit pattern (image pattern) are required especially, for the circuit substrate in these objects, the conventional circuit substrate is described below as a typical example.
In recent years, progress of information and communication technology and progress of electronic devices promote miniaturization and densification of circuit substrate, and there appears the high density multilayer circuit substrate completed by fusing thin and thick film techniques into multilayered technique. In addition, in fields of run vehicle, jet plane and rocket etc., it is pushed forward hurriedly the development of an electric device which can endure high temperature, high humidity, vibration and mine dust generated by engine system, road surface friction, and air friction etc.
In order to introduce heat resistance, damp-proof, vibration-proof and dustproof as well as miniaturization and densification electronic devices, it is requested that the circuit substrate possesses such properties. The circuit substrate is the material which is formed by the circuit pattern on the surface thereof, and in particular, a ceramics substrate is used as substrate which satisfies heat resistance and high temperature resistance.
FIG. 10 shows a manufacturing process diagram of conventional circuit substrate which is made from a ceramics substrate. In the process of (A), greensheet 2 formed by ceramic materials is arranged at the predetermined location. This greensheet is a raw material of sheet-shape formed from slurry, which is made from mixture of ceramic powder, organic solvent, organic binder and plasticizer.
In the process of (B), unexposed substrate 3 is formed by applying photosensitive paste layer 4 on the greensheet 2. At first, photosensitive paste is prepared by mixing, for example, circuit material Ag and photoresist of photosensitive agent, and then photosensitive paste layer 4 is formed by applying said photosensitive paste to the surface of the greensheet 2.
In the process of (C), a latent image of circuit pattern is formed by irradiating ultraviolet rays on photosensitive paste layer 4. Conventionally, photomask 60 is used to form the latent image. In the photomask 60, there are light-passing area 60a shown by white background and non-light-passing area 60b on shown by hatching.
The photomask 60 is opposed to the photosensitive paste layer 4, and ultraviolet radiation 62 is irradiated on the whole surface. The ultraviolet radiation 62 is intercepted in non-light-passing area 60b, and transmits only in light-passing area 60a. Therefore, in the photosensitive paste layer 4, there are formed exposed area 4a which received the ultraviolet irradiation, and unexposed area 4b which did not receive ultraviolet irradiation. In other words, the opposed area of light-passing area 60a becomes exposed area 4a, and the opposed area of non-light-passing area 60b becomes unexposed area 4b. 
In the process of (D), whole surface of photosensitive paste layer 4 is developed by spraying of developing solution 14 from developing device 12 or by dipping into developing solution. Unexposed area 4b becomes removal area 16 by removing photosensitive paste, because the latent image is not formed. On the other hand, as for exposure part 4a in which the latent image is formed, the photoresist is harden by polymerizing through developing and remains just. Therefore, unsintered circuit pattern 17 is formed on the surface of the greensheet 2.
In the process of (E), the greensheet having unsintered circuit pattern 17 is sintered at desired temperature. All the organic matter of greensheet 2 is burnt and removed by sintering, and then the remained ceramic materials are sintered to be ceramic substrate 18. At the same time, all the organic matter of unsintered circuit pattern 17 is burnt and removed, too, and the remained Ag powder becomes the uniform Ag film to form the circuit pattern 20.
In this way, circuit substrate 22 which consists of ceramics substrate 18 with circuit pattern 20 is completed. For the circuit substrate 22, it is clear that a high density circuit pattern can be provided because circuit pattern 20 is formed with photomask 60, and besides, the high temperature resistance characteristic is realized because ceramic substrate 18 is used.
This circuit substrate is excellent at a point to possess both of densification and high temperature resistance characteristic by using thin and thick film techniques and ceramic sintering technique. In addition, this circuit substrate is excellent at the point of vibration-proof and dust-proof, because a conductor circuit is integrated inside of ceramics. However, the weakest point of this circuit substrate is that the photomask is used for exposure.
The first weak point of photomask utilization is that the great cost and time are required to form the photomask. It says generally, a lot of processes are needed for production of photomask.
The photomask production begins from a pattern layout diagram appeared on the basis of a circuit design drawing. Based on the design data, a master reticle of size of 10 times is made by pattern generator. Next, the master reticle is reduced to the 1/10 size by a photo repeater, and a master mask is made by duplicate of the reduced one. A work mask which is used for actual processing is made from said master mask. Therefore, time and cost are necessary by all means, because a few days are needed to make a piece of work mask.
The second weak point of photomask utilization is that there is a limitation in precision of the pattern. An innovation is needed for making of more precise photomask, because the limit precision size of a photomask is about 1 μm.
The third weak point of photomask utilization is that the latent image cannot be formed according to the fineness of dimension of a photomask because the ultraviolet radiation is diffracted through the photomask. It is better that photomask is adhered to the photosensitive paste layer to make better exposure fineness, but the surface of the photosensitive paste layer might be injured. In other words, the contact of the photomask is denied absolutely, because the photosensitive paste surface is damaged if the photomasks come in contact with undried photosensitive paste layer. On the other hand, in the case of drying of the photosensitive paste, the production cost rises because the manufacturing process becomes complicated by a requirement of time for drying.
In there, as shown in FIG. 10(C), it is usual that photomask 60 is arranged to be estranged with only minute distance from photosensitive paste layer 4. Then, the width of unexposed section 4b becomes smaller or larger than the width of non-light-passing area 60b, because ultraviolet radiation diffracts at both end edges of non-light-passing area 60b. This means that exposure fineness of photosensitive paste layer 4 gets worse than the pattern precision of the photomask 60.
Although the weak points of conventional circuit substrate production method are described above, there are also the similar weak points in the case that the image pattern is formed on the general object surface. That is to say, an image pattern can be formed through the steps of forming photosensitive paste by mixing photoresist and colorant powder, applying the photosensitive paste to the object surface uniformly, irradiating ultraviolet to the surface through a photomask and developing. However, so far as a photomask is employed, said same weak point as the circuit substrate cannot be avoided in the case of this image pattern forming, too.
Therefore, the present invention of method for forming image on object surface including circuit substrate aims at forming of an image with high fineness and high density on a object surface by using of novel exposure method without the photomask, so that reducing of the time and cost to make photomask, shortening of exposure time of photosensitive paste layer and improving of the exposure precision are realized.